LED 조명 및 원형 공동 효과에 대한 연구: The research on the LED illumination and the effects of a cylindrical cavity

by Ui Hyung Lee (MS Candidate)

Friday Nov 11, 2011, 2:45 PM → 3:00 PM Asia/Seoul

216-1호 (제1과학관)

This paper deals with the designs of the illumination optics used for light-emitting diode(LED) and the effect of the cavity on the etendue of a light source.
Firstly, a 3 W LED was employed to achieve the high performance medical headlight. The optical design includes two lenses for high energy transmission and high illuminance. The LED headlight shows 42,000 lux with spot diameter of 80 mm at the distance of 300 mm. For comparison purpose, 5 W LED was also used to obtain the high illuminance headlight. However, the large divergence angle and large spot size of the 5 W LED limits the illuminance to 31,000 lux with increased burden on heat dissipation. The thermal images of the heat sinks indicate that the temperature of the headlight using a 3 W LED is below 50 degree C, which is suitable for medical applications.
Secondly, a 3 W LED was also employed to achieve the high performance medical headlight. The optical design included single Fresnel lens for high energy transmission, high illuminance and spot size control. The fabricated LED headlight showed 51,000 lux with spot diameter of 40 mm and 7,000 lux with spot diameter of 120 mm at the distance of 300 mm. The thermal images of the heat sinks indicated that the temperature of the headlight is 50.4 degree C, which was suitable for medical applications.
Thirdly, the paper proposes that the cylindrical cavity around a circular light source can decrease the divergence angle without changing the emission energy and source size. This result can provide a way to reduce the etendue of the light source by scrambling the rays inside the cavity with a lossless scattering surface. The experiment demonstrated that the metallic cavity around the surface source reduced the divergence angle. However, the metallic surface also absorbed quite a large portion of the light energy. The Lambertian nature of the sidewall surface changed the directions of the rays into horizontal directions. It increased the number of reflections inside the cavity and amplified the small amount of absorption at a single reflection. This effect of the cavity on the etendue of the light source can contribute to providing more design flexibility in various lighting applications.

Thesis Advisor: Prof. Young-Gu Ju